1. Field of the Invention
The present invention relates to a structured fibrous gasket. More particularly the fibrous gasket sheet has at least one bolt area in the structure, the bolt area having a tapered densification.
Gasketing is required to provide a seal between flange areas of motors. A good seal must be achieved initially, and in addition to this, the seal must be maintained to give the gasket a good seal throughout its life. To maintain a seal, retaining bolt stretch is important. Thus, a further requirement is that the gasket should retain bolt stretch during use. The bolt areas of the gasket are known to have problems such as the retention of bolt stretch and thereby not providing an adequate long term seal to the flange.
It has been found that when inserts are put into the gasket bolt areas to add at least partial densification to the gasket structure then an appropriate seal and good bolt stretch retention can be achieved in the gasket. References can be found which teach the use of inserts and washers in the bolt locations of gaskets. In particular, U.S. Pat. No. 3,863,936 teaches that the bolt hole areas are densified in part by embedded steel washers in the gasket body to minimize carburetor flange flexing and maintain high torque retention under heat. According to this reference, when the clamping bolts are brought down upon the densified bolt hole areas with an embedded washer, they provide appropriate sealing, conformability and deflection characteristics.
Another reference is U.S. Pat. No. 4,535,999. This patent teaches that a grommet can be positioned in a clear-through opening, the grommet being a sealing member which comprises a metallic insert having upper and lower surfaces and compressible material on each of the upper and lower surfaces.
When such inserts are used around the bolt holes of gaskets, however, the gasket disadvantageously lacks conformity to the flange. This lack of conformity to the flange, of course, results in a lower sealing ability. It would be advantageous to provide a gasket structure which has good bolt stretch retention and provides a superior seal to the flange.
It is, therefore, an object of the present invention to provide a gasket structure with good bolt stretch retention and good sealing ability. Other objects will be apparent from this description to those of ordinary skill in the art.